[dahy-uh-tuh m, -tom]


any of numerous microscopic, unicellular, marine or freshwater algae of the phylum Chrysophyta, having cell walls containing silica.

Nearby words

  1. diathermanous,
  2. diathermic,
  3. diathermy,
  4. diathesis,
  5. diathetic,
  6. diatomaceous,
  7. diatomaceous earth,
  8. diatomic,
  9. diatomite,
  10. diatonic

Origin of diatom

1835–45; < New Latin Diatoma originally a genus name, feminine noun based on Greek diátomos cut in two. See dia-, -tome

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for diatom

British Dictionary definitions for diatom



any microscopic unicellular alga of the phylum Bacillariophyta, occurring in marine or fresh water singly or in colonies, each cell having a cell wall made of two halves and impregnated with silicaSee also diatomite

Word Origin for diatom

C19: from New Latin Diatoma (genus name), from Greek diatomos cut in two, from diatemnein to cut through, from dia- + temnein to cut

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for diatom



1845, coined from Greek diatomos "cut in two," from diatemnein "to cut through," from dia- "through" (see dia-) + temnein "to cut" (see tome). So called because they typically appear to have been cut in half. Related: Diatomic.

Online Etymology Dictionary, © 2010 Douglas Harper

Science definitions for diatom



Any of various one-celled aquatic organisms of the class Bacillariophyceae that have hard bivalve shells (called frustules) composed mostly of silica, can perform photosynthesis, and often live in colonies. They make up a large portion of the marine plankton and are an important food source for many aquatic animals. The skeletal remains of diatoms are the main constituent of diatomite.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.